1. Technical Field
The invention relates to improving uplink feedback signaling.
2. Discussion of Related Art
Abbreviations3GPPThird generation partnership programA/N ACK/NACKACKAcknowledgementBERBit Error RatioBLERBlock Error RatioBPSKBinary Phase Shift KeyingCMCubic MetricDLDownlinkCQIChannel Quality IndicatorCRCCyclic Redundancy CheckECREffective Coding RateEDCHEnhanced Dedicated ChannelENSREstimated Signal to Noise RatioFBFeedbackHARQ Hybrid Automatic Repeat RequestLTELong Term EvolutionMCSModulation and Coding SchemeMIMOMultiple-Input Multiple-OutputNACKNegative ACKPAPRPeak to Average Power RatioPARPeak-to-average ratioPUSCHPhysical Uplink Shared ChannelQAMQuadrative Amplitude ModulationQoSQuality of ServiceQPSK Quadrative Phase-Shift KeyingRRCRadio Resource ControlRUResource UnitSDMASpace Division Multiple AccessSIMOSingle-Input Multiple-OutputSINRSignal-to-Interference and Noise RatioSNRSignal-to-Noise RatioTDMTime Division MultiplexingTFCITransport Format Combination IndicatorTFCTransport Format CombinationTTITransmission Time IntervalULUplinkUTRANUniversal Terrestrial Radio Access NetworkVoIPVoice over Internet Protocol
This invention arose in the context of developments underway in the UL part of UTRAN long term evolution (LTE) often referred as 3.9 G but is not limited to that context. Even though the uplink is the focus of this disclosure, the invention is not necessarily limited to the uplink.
For UMTS, multicodes are used for both the control and data channels and such is not available in LTE due to bad PAPR. The signaling has to be transmitted as inband signaling with the data transmission.
More particularly, the invention arose during consideration of resource allocation for non-data-associated control signals transmitted with UL data on the PUSCH (Physical Uplink Shared Channel). These control signals include ACK/NACK due to the DL transmission and CQI reporting which can be either periodic or scheduled.
In RAN1#46bis, it has been agreed that data non-associated uplink control signaling is to be multiplexed with UL data with time division multiplexing (TDM). Detailed operations have not been discussed yet in 3GPP.
As suggested above, although the invention is not limited to the specific context in which it arose, it proceeds from consideration of the basic problem of how to divide the available physical resources (i.e., symbol space and transmission power) between data-non-associated control and data channels in LTE UL system. Information about the symbol space division must be pre-known at both ends of the radio link in order to perform correct rate matching/de-matching and encoding/decoding operations for different channels. Although not limited to such a scenario, it is noted that in the LTE UL system, the eNode-B (base station) has to be in charge of the resource split between the control and data parts and signaling this information to the UE. This is mainly due to the following things:                Data-associated control signaling is not supported in LTE UL. Therefore UE cannot signal transport format indication to the eNode B.        Blind detection is not feasible in UL, not only from the receiver complexity point of view but also taking into account the fact that CRC may not be available so there is no handy criterion on which to base the decision which of multiple possible formats was actually transmitted.        
A second problem is how to optimize the performance of data-non-associated control signaling. It is noted that power control will set the SINR target of PUSCH according to the data channel. Therefore, the control channel has to adapt to the SINR operation point set for data. Control signals have typically much tighter delay requirements. Furthermore, control signaling benefits neither from the fast link adaptation nor the HARQ. Therefore the coding for data-non-associated control signaling needs to be done with somewhat more margin.
A third problem relates to different performance requirements of UL data and control signals.                ACK/NACK BER should be about 0.1% (no HARQ)        CQI BLER should typically be less than 10% (no HARQ)        BLER of UL data channel(s) varies usually between 10% and 30% (depending on the HARQ operation point).        
One way to adjust the available resources between control and data parts is to apply different power offset values for them. There are two main disadvantages regarding this power offset method:                PAR problem: It has been shown in [R1-072224] that PAR and CM are increased when higher power is configured for control rather than for data. [R1-072224] recommends that the control power should be limited not to exceed the data power. Furthermore, it is not possible to increase the Tx power of control signaling, when the UE is transmitting with full power (i.e., located at the cell edge). So power increase is inefficient in providing adequate quality in several cases in practice.        It is also noted that from resource utilization point of view, power reduction is not too economic since all the available power resources won't be utilized any more. This is equivalent to a waste of capacity.        
R1-071000 presents another prior art technique, where the symbol space of data-non-associated control channels is tied to the data modulation used by UL data channel. This is simply a consequence of the fact that the number of bits that is conveyed with a symbol depends on the data modulation: QPSK, 16QAM and 64 QAM carry 2, 4 and 6 bits respectively, therefore the number of symbols needed to carry a given number of bits from coding of data-non-associated control signaling depends on the modulation used. The applied symbol space corresponding to different data modulations is signalled to the UE by means of higher layer signalling (RRC signalling).
A problem related to this technique is that it is unable to guarantee the QoS of the data-non-associated control signaling. It is noted that the BLER target of the UL data channel may vary quite a lot, depending on many issues and parameters:                Different services will have different QoS requirements anyway (e.g., delay performance, BLER). Therefore, it is problematic to tie the symbol space of data-non-associated control channel only for the MCS used by UL data.        Performance of data-non-associated control signalling depends not only on the SINR but also the number of RUs allocated for UL data. For that reason, the symbol space allocated for the control channel should vary also according to the bandwidth.        Propagation environment may change quite rapidly. RRC signaling may not be able to track these changes fast enough.        Feasibility of this method depends also on the UL HARQ scheme (adaptive vs. non-adaptive)        
Therefore, it is difficult to provide sufficient quality for control signals if the symbol space of data-non-associated control is tied only to the modulation and coding scheme (MCS) used by UL data.
The disclosure that follows deals with transport format selection of data-non-associated control signals transmitted with UL data. Also disclosed are some special, non-limiting cases of transport format selection for UL data transmission.